Energy Deposition of MeV Electrons in Compressed Fast-Ignition Targets C. K. Li, F.H. Séguin and R. D. Petrasso MIT Annual Meeting of FSC at Laboratory for Laser Energetics January, 2006  E (keV/μm 3 ) Uniform model This model MIT

Summary  Classical Coulomb collision dominates interactions of energetic electron in dense core of fast-ignition targets  Electron energy loss, penetration and scattering are inextricably coupled together  Blooming and straggling effects lead to a non-uniform, extended region of energy deposition  This result significantly changes the energy deposition profiles regardless of the electron beam radius MIT

 n b /n e ~10 -2 n b /n e > : self fields, i nstabilities, …. n b /n e < : scattering Laser For the interior of a FI capsule, scattering dominates other mechanisms in affecting energy deposition, beam blooming, and straggling MIT

Electron scattering must be included in calculating the energy deposition 1 MeV e 14.1  m 18.8 MeV p MIT

e plasma BB BB RR RR Scattering reduces the electron linear penetration, and it results in longitudinal straggling and beam blooming Combine all these effects, the energy deposition profile is modified

The effects of energy loss and scattering must be treated with a unified approach Scattering Energy loss Where: Moller Rutherford MIT

Scattering are insensitive to plasma screening models  1 (E) Plasma screening: D ---- Debye length d ---- inter-particle distance TF ---- Thomas-Fermi  = 300 g/cm 3 ; T e = 5 keV scattering Energy loss

Multiple scattering enhances electron linear-energy deposition  = 300 g/cm 3 ; T e = 5 keV where MIT

The qualitative features of this model --- penetration, blooming and straggling --- are replicated by Monte Carlo calculations for solid DT 1 MeV e This modelMonte Carlo MIT

For electrons with low energies, blooming and straggling become important even with little energy loss (  E) RR  E ~60% STDV (  m)  E ~40%  E ~25% BB BB 10 MeV 1 MeV 0.1 MeV RR BB RR MIT

An effective Bragg peak results from the effects of blooming and straggling Conventional Bragg peak results from the velocity match RR RR Conventional Bragg peak Effective Bragg peak MIT dE/d(  R)

Effects of scattering are integrated in a simple formula for energy deposition Where: Stopping power Energy straggling Beam blooming Range straggling MIT

Combining these effects, electron energy deposition is notably different than the uniform model prediction r b = 10 μm r b = 20 μm  E (keV/μm 3 ) r b = 1 μm r b = 5 μm Uniform model This model  Density (g/cm 3 ) Distance (  m) MeV e MIT

Summary  Classical Coulomb collision dominates interactions of energetic electron in dense core of fast-ignition targets  Electron energy loss, penetration and scattering are inextricably coupled together  Blooming and straggling effects lead to a non-uniform, extended region of energy deposition  This result significantly changes the energy deposition profiles regardless of the electron beam radius MIT